The amount of drugs brought into the UK by courier is not negligible - it is currently between four and five tons a year - but compared to the large consignments smuggled by road and sea, it is not a huge amount.

But it is a high-risk enterprise for the "mules", as they are known.

First, there is the danger to health.

Many secrete substances like cocaine by swallowing it or inserting it into body orifices (which explains the soubriquet, "stuffers and swallowers").

Condoms and latex gloves are some of the means used to wrap the drug before it is swallowed.

Not infrequently, a dreadful accident occurs mid-flight and the package bursts inside the victim.

Last October, a middle-aged woman died on a flight from Kingston, Jamaica to Heathrow when one of the 55 packages she had swallowed burst.

At about the same time, a 27-year-old man on a London-bound flight from Jamaica also died when pure cocaine seeped uncontrollably into his stomach.

The second danger is imprisonment.

The number of British couriers jailed in the Caribbean has risen substantially in recent years.

100 Britons held

More than 100 are being held in Jamaica.

In Britain tough sentences for couriers have led to the jailing of many hundreds, especially women.

Many are single mothers who are not only deprived of their freedom but their children too.

Of course, what drives this trade is money.

There is the economics of the cocaine market which, currently, has Britain at the top of western league for price.

Big mark-up

Every kilo smuggled into the country has a street value of up to £125,000 - a mark-up of around £100,000 on the wholesale value.

It is many times the price fetched in the United States where the market was saturated some years ago.

There is also the grinding poverty of Kingston which drives many people to look for a cash solution to their problems: they can earn around £3,000 for a successful smuggling trip to London.

London-based couriers, with links to the Caribbean, can also be easily tempted.

Some Customs and immigration staff at London¿s airports complain, privately, that the emphasis on intelligence-led surveillance has reduced the number of officers available to check passengers.

There is said to be a particular problem at Heathrow Terminal Three.

Equally, the number of Jamaicans stopped from entering the UK is already higher than for any other Commonwealth country and any suspicion of a "witch-hunt" would lead to cries of racism.